Recently, different synchronous networks have been or are going to be deployed in many countries around the world, especially, TDD (Time Division Duplexing) networks, as typical synchronous network, have developed quickly. In some areas coexistence between two or more synchronous networks appears to be inevitable. For example, as one of the international 3G standards, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) standard has been widely deployed by China Mobile in China, and it is expected that Time Division-Long Term Evolution (TD-LTE), as an evolution of TD-SCDMA, will coexist with TD-SCDMA in future. Similarly, Personal Handyphone System (PHS) network and eXtended Global Platform (XGP) network may coexist in Japan; still, TD-LTE and Wimax networks may coexist in Southeast Asia. Interoperation between the coexisting TDD networks is a key feature to maintain session continuity.
Air-interface timing synchronization in both downlink and uplink is essential to TDD system. However, in the conventional solution for coexisting networks, timing synchronization information is not shared between networks. For example, a User Equipment (UE) that supports two coexisting different networks may wish to perform a cell handover or reselection from one network to another, as called an Inter-Radio Access Technology (IRAT) handover or reselection. The UE has already performs downlink and/or uplink timing synchronization with the source cell, but without the timing synchronization information, it has to redo the downlink and/or uplink timing synchronization with the target cell, which will increase control plane latency and user plane interruption time.